Methods of forming refractory metal silicide components and methods of restricting silicon surface migration of a silicon structure

ABSTRACT

Methods of forming refractory metal silicide components are described. In accordance with one implementation, a refractory metal layer is formed over a substrate. A silicon-containing structure is formed over the refractory metal layer and a silicon diffusion restricting layer is formed over at least some of the silicon-containing structure. The substrate is subsequently annealed at a temperature which is sufficient to cause a reaction between at least some of the refractory metal layer and at least some of the silicon-containing structure to at least partially form a refractory metal silicide component. In accordance with one aspect of the invention, a silicon diffusion restricting layer is formed over or within the refractory metal layer in a step which is common with the forming of the silicon diffusion restricting layer over the silicon-containing structure. In a preferred implementation, the silicon diffusion restricting layers are formed by exposing the substrate to nitridizing conditions which are sufficient to form a nitride-containing layer over the silicon-containing structure, and a refractory metal nitride compound within the refractory metal layer. A preferred refractory metal is titanium.

PATENT RIGHTS STATEMENT

This invention was made with Government support under Contract No.MDA972-92-C-0054 awarded by Advanced Research Projects Agency (ARPA).The Government has certain rights in this invention.

TECHNICAL FIELD

This invention relates to methods of forming refractory metal silicidecomponents and methods of restricting silicon surface migration of anetched silicon structure relative to a surface of an underlyingrefractory metal layer.

BACKGROUND OF THE INVENTION

Fabrication of semiconductor devices involves forming electricalinterconnections between electrical components on a wafer. Electricalcomponents include transistors and other devices which can be fabricatedon the wafer. One type of electrical interconnection comprises aconductive silicide line the advantages of which include higherconductivities and accordingly, lower resistivities.

Typically, conductive silicide components can be formed by blanketdepositing a layer of refractory metal over the wafer and then blanketdepositing a layer of silicon over the refractory metal layer. Forexample, referring to FIG. 1, an exemplary wafer fragment in process isshown generally at 10 and includes a substrate 12. Exemplary materialsfor substrate 12 comprise suitable semiconductive substrate materialsand/or other insulative materials such as SiO₂. As used is thisdocument, the term "semiconductive substrate" will be understood to meanany construction comprising semiconductive material, including, but notlimited to, bulk semiconductive materials such as a semiconductive wafer(either alone or in assemblies comprising other materials thereon), andsemiconductive material layers (either alone or in assemblies comprisingother materials). The term "substrate" refers to any supportingstructure, including, but not limited to, the semiconductive substratesdescribed above. A refractory metal layer 14 is formed over substrate 12followed by formation of a layer 16 of silicon.

Referring to FIG. 2, layer 16 is patterned and etched to form aplurality of silicon-containing structures 17. Silicon-containingstructures 17 constitute structures from which electrical interconnectsare to be formed relative to wafer 10. The etching of thesilicon-containing structures defines a silicon-containing structuredimension d₁ and a silicon-containing structure separation distance d₂.In the illustrated example, d₁ is substantially equal to d₂. Suchrelationship between d₁ and d₂ results from a desire to use as much ofthe wafer real estate as is available. Accordingly, the spacing betweenthe silicon-containing structures reflects a critical dimension which isa function of the limitations defined by the photolithography technologyavailable. The goal is to get the silicon-containing structures as closeas possible to conserve wafer real estate.

Referring to FIG. 3, substrate 12 is exposed to suitable conditions tocause a reaction between the refractory metal layer 14 and thesilicon-containing structures 17. Typical conditions include a hightemperature annealing step conducted at a temperature of about 675° C.for about 40 seconds. Subsequently, the unreacted refractory metal isstripped from the wafer. The resulting refractory metal silicidecomponents or lines are illustrated at 18 where the resulting linedimensions d₁ ' can be seen to be larger than the silicon-containingstructure dimensions d₁ (FIG. 2) from which each was formed.Accordingly, the relative spacing or separation between the lines isillustrated at d₂ '. With the attendant widening of the silicidecomponents or lines, the separation distance between them iscorrespondingly reduced. A major cause of this widening is the diffusivenature of the silicon from which the FIG. 2 silicon-containingstructures are formed. That is, because silicon is highly diffusive innature, the formation of the FIG. 3 silicide components causes a surfacemigration of the silicon relative to the underlying substrate. In thepast, when device dimensions were larger, the migration of siliconduring silicide formation was not a problem. Adequate spacing betweenthe resulting silicide lines ensured that there would be much lesschance of two or more components shorting together. However, as devicedimensions grow smaller, particularly at the 0.35 μm generation andbeyond, there is an increased chance of shorting. This is effectivelyillustrated in FIG. 4 where two refractory metal components 19 can beseen to engage one another and hence short together at 20.

This invention grew out of concerns associated with forming silicidecomponents. This invention also grew out of concerns associated withimproving the integrity of electrical interconnections as devicedimensions grow ever smaller.

SUMMARY OF THE INVENTION

Methods of forming refractory metal silicide components are described.In accordance with one implementation, a refractory metal layer isformed over a substrate. A silicon-containing structure is formed overthe refractory metal layer and a silicon diffusion restricting layer isformed over at least some of the silicon-containing structure. Thesubstrate is subsequently annealed at a temperature which is sufficientto cause a reaction between at least some of the refractory metal layerand at least some of the silicon-containing structure to at leastpartially form a refractory metal silicide component. In accordance withone aspect of the invention, a silicon diffusion restricting layer isformed over or within the refractory metal layer in a step which iscommon with the forming of the silicon diffusion restricting layer overthe silicon-containing structure. In a preferred implementation, thesilicon diffusion restricting layers are formed by exposing thesubstrate to nitridizing conditions which are sufficient to form anitride-containing layer over the silicon-containing structure, and arefractory metal nitride compound within the refractory metal layer. Apreferred refractory metal is titanium.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic sectional view of a semiconductor waferfragment at one prior art processing step.

FIG. 2 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 1.

FIG. 3 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 2.

FIG. 4 is a view of the FIG. 1 wafer fragment at a processing stepsubsequent to that shown by FIG. 3.

FIG. 5 is a diagrammatic sectional view of a semiconductor waferfragment at one processing step in accordance with the invention.

FIG. 6 is a view of the FIG. 5 wafer fragment at a processing stepsubsequent to that shown by FIG. 5.

FIG. 7 is a view of the FIG. 5 wafer fragment at a processing stepsubsequent to that shown by FIG. 6.

FIG. 8 is a view of the FIG. 5 wafer fragment at a processing stepsubsequent to that shown by FIG. 7.

FIG. 9 is a view of the FIG. 5 wafer fragment at a processing stepsubsequent to that shown by FIG. 8.

FIG. 10 is a view of the FIG. 5 wafer fragment at a processing stepsubsequent to that shown by FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws "to promote the progressof science and useful arts" (Article 1, Section 8).

Referring to FIG. 5, a semiconductor wafer fragment, in process, isshown generally at 22 and includes substrate 24. Substrate 24 canconstitute a semiconductive substrate or an insulative substrate. Arefractory metal layer 26 is formed over substrate 24 and includes anouter exposed surface 28. An exemplary and preferred material for layer26 is titanium. Other refractory metal materials can, of course, beutilized. An exemplary thickness for layer 26 is about 300 Angstroms.

Referring to FIG. 6, a silicon-containing layer 30 is formed over outersurface 28 of refractory metal layer 26. An exemplary thickness forlayer 30 is about 1100 Angstroms.

Referring to FIG. 7, layer 30 is patterned and etched into a pluralityof silicon-containing structures 32 over the substrate. Individualstructures 32 have respective outer surfaces 34. Individual outersurfaces 34 are, in the illustrated example, defined by respectivestructure tops 36, and respective structure sidewalls 38. Adjacentstructures have respective sidewalls which face one another. Individualstructures 32 also include respective silicon-containing portions 40which are disposed proximate refractory metal layer outer surface 28. Ina preferred implementation, silicon-containing structures 32 havestructure dimensions d₁ ", and adjacent silicon-containing structures 32constitute respective pairs of structures having first lateralseparation distances or spacings d₂ " (illustrated for the left-mostpair of structures). In accordance with this implementation, d₁ " and d₂" are no greater than about 0.35 μm.

Referring to FIG. 8, substrate 24 is exposed to conditions which areeffective to form silicon diffusion restricting layers 42 over at leastsome of the silicon-containing portions 40 proximate outer surface 28 ofthe refractory metal layer 26. Preferably, the silicon diffusionrestricting layers 42 cover the entirety of the individualsilicon-containing structures 32 and are formed to a relative thicknessof no less than about 10 Angstroms. Even more preferably, the thicknessof layers 42 is between about 10 to 20 Angstroms. Accordingly, therespective sidewalls of the individual structures 32 are covered withrespective silicon diffusion restricting layers. According to anotheraspect of the invention, the conditions which are effective to formsilicon diffusion restricting layers 42 are also effective to formsilicon diffusion restricting layers or regions 44 over or withinrefractory metal layer 26. Exemplary and preferred elevationalthicknesses of layers 44 are less than or equal to about 50 Angstroms.Accordingly, layers 42 constitute first silicon diffusion restrictingstructures or layers and layers/regions 44 constitute second silicondiffusion restricting structures or layers.

In a preferred implementation, the silicon-containing structures 32 andthe refractory metal layer surface 28 are exposed to nitridizingconditions in a common step. Such conditions are preferably effective tocover the respective silicon-containing structures withnitride-containing material (layers 42) such as silicon nitride, andform nitride-containing material layers 44 within the refractory metallayer between the silicon-containing structures. In this implementation,nitride-containing material layers 44 constitute a refractory metalnitride compound such as TiN_(X), with titanium being a preferredrefractory metal material as mentioned above. Exemplary and preferrednitridizing conditions in a cold wall reactor comprise a low pressure(about 1 Torr), low temperature N₂ /H₂ atomic plasma at a reactor powerof 200 Watts to 800 Watts. Flow rates are respectively about 100 to 300sccm for N₂ and 450 sccm for H₂. Addition of H₂ into N₂ plasma reducesif not eliminates oxidation of the exposed refractory metal surface.Suitable temperature conditions for such nitridizing includetemperatures between about 250° C. to 450° C., with temperatures between375° C. and 400° C. being preferred. Preferred exposure times under suchconditions range between 30 to 60 seconds. The above processingconditions are only exemplary and/or preferred processing conditions.Accordingly, other processing conditions or deposition techniques arepossible.

Referring to FIGS. 9 and 10, and after the formation of the abovedescribed silicon diffusion restricting layers, substrate 24 is annealedto a degree sufficient to react at least some of the material of thesilicon-containing structures with at least some of the refractory metalmaterial. FIG. 9 shows an intermediate substrate construction duringsuch annealing thereof. Suitable processing conditions include atemperature of about 675° C. for about 40 seconds in N₂. Accordingly,such forms respective refractory metal silicide components 46. Silicidecomponents 46 can include respective silicide portions 47 and unreactedsilicon portions 48. After forming components 46, substrate 24 can besubjected to a stripping step comprising a mix of ammonia and peroxide.In a preferred implementation, such refractory metal silicide componentsconstitute conductive lines which electrically interconnect variousintegrated circuitry devices or portions thereof. In an exemplary andpreferred implementation, components 46 constitute at least a portion ofa local interconnect for a static random access memory cell. In theillustrated example, the silicon diffusion restricting layers areeffective to restrict silicon lateral diffusion during the annealingstep just mentioned. Accordingly, with silicon surface and otherdiffusion reduced, if not eliminated, the respective silicide components46 have a second lateral distance or spacing d₂ " therebetween which issubstantially the same as the FIG. 7 first lateral distance or spacingd₂ ". In processing regimes where a critical dimension of 0.35 μm is adesign rule, such second lateral distance would be about 0.35 μm.Accordingly, line dimensions d₁ " are substantially equal to lateraldistance or spacing d₂ " and do not meaningfully varying from the FIG. 7pre-annealing dimensions or spacings.

The above described methodology enables refractory silicide componentsto be formed which are substantially free from lateral silicon diffusionduring salicidation. Thus, closer relative spacing of such componentscan be achieved with risks associated with grounding or shorting of thecomponents reduced.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

What is claimed is:
 1. A method of forming a refractory metal silicidecomponent comprising:forming a refractory metal layer over a substrate,the refractory metal layer having an exposed surface; forming asilicon-containing structure over a portion of the exposed surface ofthe refractory metal layer, the silicon-containing structure having anouter surface, the outer surface having a surface portion proximate therefractory metal layer; forming a silicon diffusion restricting layerover at least some of the proximate surface portion and a silicondiffusion restricting region within the refractory metal layer; andafter forming the silicon diffusion restricting layer and the silicondiffusion restricting region, annealing the substrate to cause asilicide forming reaction between at least some of the refractory metallayer and at least some of the silicon-containing structure.
 2. Themethod of claim 1, wherein the forming of the silicon diffusionrestricting layer comprises forming the layer over the entirety of theproximate surface portion.
 3. The method of claim 1, wherein the formingof the silicon diffusion restricting layer comprises forming the layerto have a relative thickness of no less than about 10 Angstroms.
 4. Themethod of claim 1, wherein the forming of the silicon diffusionrestricting layer comprises forming the layer to have a relativethickness of between about 10 to 20 Angstroms.
 5. The method of claim 1,wherein the forming of the silicon diffusion restricting layer comprisesexposing the substrate to temperature conditions of between about 250°C. to 450° C. in the presence of nitrogen.
 6. The method of claim 5,wherein the exposing of the substrate comprises exposing the substrateto atomic nitrogen and atomic hydrogen.
 7. The method of claim 6,wherein the atomic nitrogen and the atomic hydrogen comprise an atomicplasma.
 8. The method of claim 1, wherein the forming of the silicondiffusion restricting layer comprises exposing the substrate totemperature conditions of between about 375° C. to 400° C. in thepresence of nitrogen.
 9. The method of claim 1, wherein the refractorymetal silicide component comprises a conductive line which constitutesat least a portion of a local interconnect for a static random accessmemory cell.
 10. A method of forming a refractory metal silicidecomponent comprising:forming a refractory metal layer over a substrate,the refractory metal layer having an outer surface; forming asilicon-containing structure over a portion of the refractory metallayer outer surface, the silicon-containing structure having asilicon-containing portion proximate an exposed portion of therefractory metal layer outer surface; forming a silicon diffusionrestricting layer over the silicon-containing portion and a silicondiffusion restricting region within the exposed portion of therefractory metal layer; and after forming the silicon diffusionrestricting layer and silicon diffusion restricting region, annealingthe substrate to cause a reaction between at least some of therefractory metal layer and at least some of the silicon-containingstructure to at least partially form a refractory metal silicidecomponent.
 11. The method of claim 10, wherein the forming of thesilicon-containing structure comprises:forming a layer comprisingsilicon over the refractory metal layer outer surface; and etching thelayer to define the silicon-containing structure having a sidewall atleast a portion of which constitutes the silicon-containing portionproximate the refractory metal layer outer surface.
 12. The method ofclaim 10, wherein the forming of the silicon diffusion restrictingregion comprises forming the region to have a elevational thicknesswithin the refractory metal layer less than or equal to about 50Angstroms.
 13. The method of claim 10, wherein the forming of thesilicon diffusion restricting layer comprises forming the layer to havea thickness over the silicon-containing portion of between about 10 to20 Angstroms.
 14. The method of claim 10, wherein the forming of thesilicon-containing structure comprises:forming a layer comprisingsilicon over the refractory metal layer outer surface; and etching thelayer to define the silicon-containing structure having a sidewall atleast a portion of which constitutes the silicon-containing portionproximate the refractory metal layer outer surface; and wherein theforming of the silicon diffusion restricting layer and the silicondiffusion restricting region comprises forming the layer and the regionin a common step, the region to have an elevational thickness within therefractory metal layer of about 50 Angstroms, and the layer to have athickness over the silicon-containing portion of between about 10 to 20Angstroms.
 15. The method of claim 10, wherein the forming of thesilicon-containing structure comprises:forming a layer comprisingsilicon over the refractory metal layer outer surface; and etching thelayer to define the silicon-containing structure having at least onesidewall at least a portion of which constitutes the silicon-containingportion proximate the refractory metal layer outer surface; and whereinthe forming of the silicon diffusion restricting layer comprises formingthe restricting layer over the entirety of the silicon-containing line.16. The method of claim 10, wherein the forming of the silicon diffusionrestricting layer comprises exposing the substrate to temperatureconditions of between about 250° C. to 450° C. and in the presence ofnitrogen and forming a silicon diffusion restricting layer over thesilicon-containing portion comprising silicon nitride and having arelative thickness of between about 10 to 20 Angstroms.
 17. A method offorming a refractory metal silicide component comprising:forming arefractory metal layer over a substrate; forming a silicon-containinglayer over the refractory metal layer; etching the silicon-containinglayer to form a silicon-containing structure over the refractory metallayer; forming a nitride-containing layer over at least some of thesilicon-containing structure; forming a refractory metal nitride regionwithin the refractory metal layer proximate the silicon-containingstructure; and annealing the substrate sufficiently to at leastpartially form a refractory metal silicide component proximate thesilicon-containing structure.
 18. The method of claim 17, furthercomprising forming a refractory metal nitride region within therefractory metal layer proximate the silicon-containing structure,wherein the forming of the nitride-containing layer and the forming ofthe refractory metal nitride region comprise a common step.
 19. Themethod of claim 17, further comprising forming a refractory metalnitride region within the refractory metal layer proximate thesilicon-containing structure, wherein the forming of thenitride-containing layer and the forming of the refractory metal nitrideregion comprise a common step, the common step comprising exposing thesubstrate to temperature conditions between about 250° C. to 450° C. inthe presence of nitrogen and for a duration sufficient to:form anitride-containing layer to a thickness of about 10 to 20 Angstroms; andform a refractory metal nitride compound having an elevational thicknessof about 50 Angstroms.
 20. A method of forming a plurality of refractorymetal silicide components comprising:providing a substrate; forming arefractory metal layer over the substrate; forming a silicon-containinglayer over the refractory metal layer; etching the silicon-containinglayer to form at least two distinct silicon-containing structures havingrespective sidewalls which face one another and define a first lateralspacing therebetween; forming a silicon diffusion restricting layer overthe structures' respective sidewalls; forming a refractory metal nitrideregion received within the refractory metal layer between the twosilicon-containing structures; and annealing the substrate sufficientlyto at least partially form respective refractory metal silicidecomponents having a second lateral spacing therebetween which issubstantially the same as the first lateral spacing.
 21. The method ofclaim 20, wherein the forming of the silicon diffusion restricting layerand the forming of the refractory metal nitride region comprise at leastone common step.
 22. The method of claim 20, wherein the forming of thesilicon diffusion restricting layer comprises exposing the substrate totemperature conditions in the presence of nitrogen sufficient to form asilicon diffusion restricting layer comprising silicon nitride.
 23. Themethod of claim 20, wherein the forming of the silicon diffusionrestricting layer and the forming of the refractory metal nitride regioncomprise at least one common step, and the forming of the silicondiffusion restricting layer comprises exposing the substrate totemperature conditions in the presence of nitrogen sufficient to form asilicon diffusion restricting layer comprising silicon nitride andhaving a thickness of between about 10 to 20 Angstroms.
 24. The methodof claim 20, wherein the forming of the silicon diffusion restrictinglayer and the forming of the refractory metal nitride region comprise atleast one common step, and the forming of the refractory metal nitrideregion comprises exposing the substrate to temperature conditions in thepresence of nitrogen sufficient to form the region to a thickness ofabout 50 Angstroms.
 25. A method of forming a pair of refractory metalsilicide components comprising:forming a layer comprising silicon over arefractory metal material having an exposed surface; etching a pair ofsilicon-containing structures from the layer comprising silicon, thestructures having a lateral separation distance relative to one anotherof no greater than about 0.35 μm; exposing the silicon-containingstructures and the refractory metal material surface to nitridizingconditions effective to cover the pair of silicon-containing structureswith nitride-containing material, and form nitride-containing materialwithin the refractory metal material between the silicon-containingstructures; and after the exposing, reacting at least some of thesilicon-containing structures with at least some refractory metalmaterial to at least partially form respective refractory metal silicidecomponents having lateral separation distances of no greater than about0.35 μm.
 26. The method of claim 25, wherein the refractory metalmaterial comprises titanium.
 27. The method of claim 25, wherein theexposing comprises:covering the pair of silicon-containing structureswith silicon nitride to a thickness of about 10 to 20 Angstroms; andforming the nitride-containing material within the refractory metalmaterial to a thickness of about 50 Angstroms.
 28. A method ofrestricting silicon surface migration of an etched silicon structurerelative to a surface of an underlying refractory metal layercomprising:in at least one common step, exposing the silicon structureand the refractory metal layer to nitridizing conditions effective toform a layer of silicon nitride over the silicon structure, and arefractory metal nitride region received within the refractory metallayer; and after the common exposing step, exposing the siliconstructure and the refractory metal layer to conditions effective to atleast partially form a refractory metal silicide component.
 29. Themethod of claim 28, wherein the exposing of the silicon structure tonitridizing conditions forms the silicon nitride layer over the entiretyof the silicon structure.
 30. The method of claim 28, wherein theexposing of the silicon structure and the refractory metal layer tonitridizing conditions is effective to form the silicon nitride layer toa thickness of between about 10 to 20 Angstroms and form the refractorymetal nitride to a thickness of about 50 Angstroms.
 31. The method ofclaim 28, wherein the refractory metal layer comprises a titanium layer.32. The method of claim 28, wherein the refractory metal layer comprisesa titanium layer and the exposing of the silicon structure and thetitanium layer to nitridizing conditions is effective to form thesilicon nitride layer to a thickness of between about 10 to 20 Angstromsand form TiN_(x) within the titanium layer to a thickness of about 50Angstroms.
 33. The method of claim 28, wherein the exposing of thesilicon structure and the refractory metal layer to nitridizingconditions comprises exposing the same to temperature conditions betweenabout 250° C. and 450° C. for a duration effective to form the siliconnitride layer to a thickness of between about 10 to 20 Angstroms andform the refractory metal nitride region to a thickness of about 50Angstroms.
 34. The method of claim 28, wherein the refractory metallayer comprises a titanium layer and the exposing of the siliconstructure and the titanium layer to nitridizing conditions comprisesexposing the same to temperature conditions between about 250° C. and450° C. for a duration effective to form the silicon nitride layer to athickness of between about 10 to 20 Angstroms and form TiN_(x) withinthe titanium layer to a thickness of about 50 Angstroms.